The way people talk about climate change, you’d think it was the biggest disaster to hit the Earth.

You’d be wrong.

Three billion years ago there was no oxygen in the atmosphere. Life consisted of unicellular organisms for whom oxygen was toxic. Then cells that could photosynthesize arrived, and started generating oxygen. After a million years there was enough oxygen in the atmosphere to kill off most of the original organisms. So, 2 billion years ago there was a big die-off of unicellular life due to the development of photosynthesis!Fast forward to 250 million years ago. At that time a flow of magma the size of the United States oozed out over what is now Siberia, and in the process gave off huge amounts of greenhouse gases. The average temperature of the Earth increased as a result. This event is largely responsible for the biggest die-off that has ever occurred on Earth; 70 percent of all land creatures and 96 percent of all sea creatures became extinct. If you look at Earth’s temperature over the last 400,000 years, you will see it varying between about 5 degrees above our current average and about 18 degrees below our current average. During that time, in almost perfect sync, the carbon dioxide level in the atmosphere varied between about 300 and 180 parts per million.

So you might think, after considering all the above, that whatever is happening with the climate now is no big deal — this kind of stuff happens all the time!

You’d be wrong.

Human civilization goes back only about 50,000 years. During that time our culture, agriculture and cities developed. During that time, the highest temperature reached was about 2 degrees above 1900 levels and the lowest was about 2 degrees below. But we are now about to rise above that 2-degree-above level, and we're rising quickly compared to the rate of change in previous years. That temperature rise coincides with increased carbon dioxide in the atmosphere, which coincides with the rise in industrialization starting in the 1700's. It is now above 400 parts per million. This rise in temperature and carbon dioxide may not look like much but we are now in uncharted territory for human civilization.

The unicellular organisms 3 billion years ago couldn’t do anything about what was happening to their atmosphere, nor could the creatures living 250 million years ago, but we can act to reverse what is happening to our world. Bipartisan solutions are out there, and both parties in Congress have started talking about action on the climate. We need to let them know how important this is.

The science on this is clear. If we do nothing to reduce greenhouse gas emissions then temperatures will rise, causing additional sea level rise, extreme drought and flooding. These are already happening, and if we don't act they will get worse, as will massive immigration, which has already started. What is uncertain is how quickly things will deteriorate. Maybe if we act to reduce greenhouse gas emissions completely in the next 20 years things won’t get too much worse than they have already gotten, and our civilization will not be completely disrupted.

Imagine your mother and her mother both died young from heart attacks, and your doctor says you have very high cholesterol and high blood pressure. You are experiencing constant shortness of breath and you can't walk down the street without becoming exhausted. Your doctor says you must exercise daily, cut saturated fat and take a statin. You ask: "Can you say for sure that I am going to die soon from heart disease?" Your doctor says: "No, but it is very, very likely unless you immediately make the changes I suggest."